The present invention relates generally to the field of providing long term extracorporeal access to the circulatory system of a living organism. In particular, it relates to a device which is permanently implantable in the skin of an organism, and which provides a more or less permanent means of access to the organism's circulatory system.
A number of medical procedures require repeated access to a patient's vascular system. In such procedures as hemodialysis and plasmapheresis, for example, it is necessary to tap into a patient's vascular system, withdraw relatively large quantities of blood therefrom, and return the blood to the system. Frequently, in the past, it has been the practice to withdraw blood by means of a needle inserted into one blood vessel, and to return the blood by means of a needle inserted into another blood vessel. However, the treatment of many patients requires repeated withdrawals of blood over a prolonged period of time. It was found that repeated insertions of needles into the veins and arteries resulted in substantial trauma to these blood vessels. Aside from the possibility of tissue damage, there is the pain and discomfort associated with the insertion of the needles.
Thus, over the years, various devices have been developed for the purpose of providing a permanent or semi-permanent means of extracorporeal access to a blood vessel. The most common approach taken by the prior art is to provide a device which is implanted in the tissues of an organism and which provides communication between a blood vessel and the exterior of the organism's body. Typically, such devices are provided with valving means to provide, selectively, extracorporeal access to the blood vessel.
One type of implantable blood vessel access device is disclosed in U.S. Pat. No. 3,765,032 to Palma. In devices of this type, a section of a blood vessel is removed and replaced with a tube having one end in communication with a blood vessel and another end projecting through the skin. The projecting end has a valve for selectively blocking and passing blood from the blood vessel. One drawback to such devices is that their removal requires a vascular graft to replace the previously removed portion of the blood vessel. In addition, the hardware required for implanting such devices is relatively complex, and in such devices, the blood is exposed to a substantial amount of foreign material in the form of the tubing, thereby increasing the probability of thrombosis.
Another type of implantable device is disclosed in U.S. Pat. No. 3,991,756 to Snyder. In devices of this nature, a cannula is surgically implanted adjacent to a blood vessel and interfaces therewith along a longitudinal wall. One end of the cannula protrudes through the skin, and this protruding end has a sealable opening. The wall of the cannula is provided with several access openings which allow a needle inserted into the cannula to puncture the blood vessel at selected sites. While devices of this type eliminate the problems associated with repeated puncturing of the skin, they do not totally eliminate the trauma associated with repeated puncturing of the blood vessel wall.
Still another type of vascular access device which has recently been developed is illustrated in U.S. Pat. No. 4,015,601 to Bokros, et al; U.S. Pat. No. 4,092,983 to Slivenko; and U.S. Pat. No. 4,108,173 to Slivenko et al. In devices of this type, a tubular conduit is inserted into a blood vessel. The conduit is in communication with a housing which extends through the patient's skin. The conduit has an aperture which communicates with the housing, and the housing has a valving mechanism including a movable valve body with a port which is alignable with the aperture. The valve body is movable between positions of alignment and non-alignment of the aperture and the port selectively to allow access to the blood vessel from the exterior of the organism. While devices of this type are capable of providing satisfactory vascular access and sealing of the access point from contamination, the valving mechanism associated with these devices is relatively bulky and complex. Moreover, installation of the conduit by which these devices communicate with the blood vessel requires a substantial interruption of the blood vessel, and there is a great deal of structure which thus invades the interior of the blood vessel, with a resulting increase in the likelihood of thrombosis.
A more recent development in the art of blood vessel access devices is illustrated in U.S. Pat. No. 4,164,221 to Bentley et al. In devices of this type, a passageway is implanted through the skin of the patient and has one end communicating with the blood vessel wall. The other end of the passageway protrudes through the skin and is closed by means of a threaded cap. The passageway is sealed by means of a plug which can be removed and inserted by means of an attachable stem. While this approach allows a minimum invasion of the interior of the blood vessel, devices of this type necessitate a significant amount of above-skin structure which is both unsightly and uncomfortable. Moreover, the insertion and removal of the plug into and out of the passageway creates a force perpendicular to the blood vessel wall, and these forces can result in undesirable stresses being created at the site where the passageway adjoins the vessel wall and is sutured thereto. Thus, care must be taken not to insert or remove the plug before the suture site is well healed, and subsequently, insertion and removal of the plug must be done gently and carefully.
From the foregoing, it can be appreciated that there are a number of objectives which the prior art has attempted to meet in the design of intravascular access devices. For example, an important criterion has been the minimization of bulky hardware, and especially to minimize the amount of structure which invades the blood vessel. A related objective is to allow installation, and possibly removal, of the device with minimum damage to the vessel and the surrounding tissues. Moreover, it is necessary that such devices allow repeated use over prolonged periods of time without substantial trauma to the blood vessel, and that when not is use, such devices provide effective sealing of the blood vessel and the access site from the external environment. Finally, it is necessary that such devices be adapted for prolonged periods of implantation and so must be adapted to minimize discomfort to the patient.
From the foregoing discussion it can be appreciated that, while the prior art devices meet some of the foregoing objectives, none of the prior art devices discussed above meets all of these objectives.